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THE MECHANISM OF OXIDE FORMATION IN THE INITIAL STAGES OF OXIDATION
OHIO STATE UNIV RESEARCH FOUNDATION COLUMBUS
Field- mission runs were made with W and Ta emission tips reacting with residual gases in the vacuum system. Of particular interest was the speckled emission pattern from W tips which had been observed after exposure at elevated temperatures. Exposure to residual gases at lower temperatures did not produce the speckled high temperature pattern. An initially clean W tip was exposed to residual gases and gettering for 81 hours. This contaminated tip was then cleaned by heating. This cleaned tip was then exposed to residual gases at ambient temperature. Subsequent heating to about 2100 C for 60 minutes did not produce a clean tip. It has been noted that Ta emission tips are considerably more difficult to clean than W tips. Field-emission reaffirmed this observation and indicated on occasion that the emission tip produces multiple patterns. Subsequent examination of these tips in the electron microscope showed some tips contain small projections and are generally not as smooth as would be desirable. Author